Zero-Based Envelopes / "Rollover Rules" Customization

The Concept: Advanced rollover control for variable budget categories.

How It Works: Give users granular rule control over what happens to unspent funds at the end of a budget cycle. Allow categories to automatically sweep leftover money into savings, roll it over to increase next month's limit, or reset back to zero based on customized per-category policies rather than a global app-wide rule.